1. Field of the Invention
This invention relates generally to a dental hygiene device. More particularly, this invention relates to an electromagnetic power-driven toothbrush provided with improved electromagnetic-and-mechanical-coupled driving mechanisms and a novel and improved battery charging device with significantly higher charging efficiency.
2. Description of the Prior Art
Several major limitations are faced by the manufacturers and designers of conventional vibrating or rotating toothbrushes driven by forces generated with input signals of continuously pulsed or alternating electromagnetic signals. A first limitation is the difficulties in generating higher frequency of bristle movements to effectively remove dental plagues by brushing and acoustic cleaning. Conventional power driven toothbrushes typically have difficulties in providing frequency of bristle movement higher than 10,000 cycles per minutes. Technical limitations and cost considerations often prevent the frequency of a conventional automatic toothbrush to exceed a limit higher than 10,000 cycles per minute. In addition to the limitations encountered for providing higher frequencies of movement, a feature of frequency control and adjustment when implemented in conventional toothbrushes would often require more complicate electromagnetic and mechanical designs and become quite costly. Typically, the power-driven toothbrushes are provided only with on-and-off switches. Due to the cost consideration, generally, there is no user control or adjustment of brushing speed. Furthermore, as rechargeable batteries are commonly used in the automatic power-driven toothbrushes, the application of the power-driven toothbrushes is often limited by requiring long period of recharging operation. Such long hours of recharge requirement is caused by the low charging rates due to the ineffective battery charging methods commonly employed in conventional electric toothbrushes now available in the marketplace.
An example of conventional vibrating toothbrushes is disclosed by Giuliani et al. disclose in U.S. Pat. No. 5,189,751, entitled “Vibrating Toothbrush Using A Magnetic Driver” (issued on Mar. 2, 1993). The vibrating toothbrush includes a toothbrush body and a lever arm that includes toothbrush bristles. The lever arm is mounted for pivotal movement at a pivot member. FIGS. 1A to 1D are exemplary drawings from the issued patents of Giuliani, et. al for illustrating typical conventional methods of converting electric energy provided by the rechargeable battery 38 into driving forces for vibrating the lever arm 14 and the toothbrush bristles 15. As shown in FIGS. 1A to 1D, a pair of permanent magnets, e.g., magnets 44 and 46 in FIG. 1B or magnets 111 and 112 in FIG. 1D, is provided at the other end of the lever arm positioned side by side with opposite polarities. Immediately next to the pair of magnets is an electromagnet, e.g., E-core electromagnet 24 or U-shaped electromagnet 116. The electromagnet receives an alternating signals from an oscillating circuit 40 having a frequency of 150 to 400 Hz with the rechargeable battery 38 functions as a power supply for the oscillating circuit 40. As the alternating signals from the oscillator drive the electromagnets to continuously change polarities, a clockwise followed by counter-clockwise vibrations are generated because of the retraction and repulsion forces generated between the permanent magnets and the electromagnets. The driving forces generated by coupling the magnetic fields between the permanent magnets and the electromagnets are however inefficient utilization of the energy provided by the rechargeable battery. The inefficiency of energy utilization is the results of energy losses in the air gap fluxes between the permanent magnets and the electromagnets. Additionally, the maximum frequency is limited to the frequency of the oscillator. Due to the constraints of the output voltage of the rechargeable battery, the maximum frequency of the oscillator is limited. Thus a higher frequency of bristle movement is difficult to achieve because the limitation of the frequency of the oscillating circuit.
Therefore, a need still exists for a new system configuration and design method in the art of automatic power driven toothbrushes to resolve these difficulties and limitations. More particularly, this new system configuration and design approach must be able to reduce the energy loss by more directly coupling the driving mechanisms provided by the battery to the lever arm connected to the toothbrush bristles. Preferably, the driving mechanism may be provided to generate output vibrations or rotations at higher frequencies than an input frequency driven by the energy provided by the battery. In addition to providing power driven toothbrushes with higher speed of bristle movements, a need also exists to more efficiently charge the battery. With improved charging circuit of this invention, the required recharging period can then be shortened and the need to purchase several automatic toothbrushes when shared by several users in a household can be eliminated with more powerful and efficient charging circuit to charge the rechargeable battery.